Method of removing and recovering solvent from nitrocellulose explosives



UNITED STATES PATENT OFFICE.

FRED W. STETSON AND JESSE L. ESSEX, OF WILMINGTON, DELAWARE, ASSIGNORS TO E. I. DU PONT DE NEMOURS & COMPANY, OF WILMINGTON, DELAWARE, A. CORPO- BATION OF DELAWARE.

METHOD OF REMOVING AND RECOVERING SOLVENT FROM NITRDCELLULOSE Patented Oct. 11, 1921.

EXZBLOSIVES.

1,393,713. Specification of Letters Patent.

No Drawing.

To all whom it may concern Be it known that we, FRED W. STETSON and Jesse L. Essex, both citizens of the United States, and residents of l/Vilmington, in the county of New Castle and State of Delaware, have invented a certain new and useful Method of Removing and Re covering Solvent from Nitrocellulose EX- plosives, of which the following is a specification.

This invention is in the art of manufacturing nitrocellulose explosives and has more particular application to the removal and recovery of the ethyl alcohol and ethyl ether used as solvent in the colloiding of the nitrocellulose, the fresh-cut grains of powder being treated by the method embodying the invention, instead of by the usual waterdrying method, to remove the solvent from the grains, except for the desired amount of residual solvent.

As is well known the usual water-drying method of solvent recovery is very slow, the time required being about fifteen days for three-inch granulation; the costs of equipment and labor are exceedingly high, and the solvent losses are large. Other methods of removing the solvent have, therefore, been proposed but have been open to various objections, the principal one being difiicult and unsatisfactory operation and control which made the production of uniform powder doubtful and gave no means of telling just when the powder had arrived at correct shrinkage or of duplicating results with certainty. The method of the present invention avoids these and various other difficulties and, by it, powder having a high degree of uniformity can be produced, and the solvent recovered quickly and at a low cost.

One object of the invention is to provide a method whereby the solvent can be removed and recovered from nitrocellulose powder grains quickly, simply and accurately, and uniformity of the powder accurately maintained.

To this end, and also to improve generally upon methods of the character indicated, the invention consists in the various matters hereinafter described and claimed.

The method, briefly stated, is as follows First, the charge of freshly-cut grains of Application filed January 30, 1926. Serial No. 355,222.

25 to 31 (3., the washing being continued until the solvent remaining in the powder is such that the desired amount of. residual solvent will be present in the powder upon completion of the treatment according to the present method, that is, the washing is continued until the remaining solvent corresponds to the desired residual solvent, this being conveniently done by continuing the washing until the ether content .of the alcohol-ether liquid flowing off is reduced to an amount indicating that the said corresponding amount of solvent remains in the powder; thisliquid is collected and the ether distilled off, leaving the ether-free alcoholic solution ready, after cooling, for reuse in the treatment of the charge being treated or of subsequent charges. Second, and upon discontinuance of the alcohol washing, the alcohol is drained from the powder. Third, the powder is washed with a flow of water, at a temperature below the boiling point of ether and preferably between 28 and 32 (1, to remove alcohol retained on the surface of, and within the perforations of, the powder after the before-mentioned draining, the washing being continued until the residual solvent is reduced to the amount desired in the finished powder and it being desirable that the alcohol content of the water at the end of the washing be under 1%; the liquid flowing off is collected and the alcohol recovered, the slop being run to the sewer, or cooled for reuse with the charge being treated or with subsequent charges. Fourth, the powder is air dried in order to reduce the moisture content to the desired quantity.

single step of washing with alcohol while constantly diluting the alcohol with water. One of these difiiculties is that of separating the solvent into its components by. distillation, due to the formation of an admixture; another is-that of having to rectify from the water the entire amount of alcohol used. By the use of relatively low temperatures for the alcohol and the water the solvent losses are reduced to a minimum, control is made easy, and the deleterious effect of hot alcohol on the appearance of powder is avoided (powder treated with hot alcohol being white upon drying). Also, the time of treatment called for b the present method is but about 2 days, rom the starting of the treatment of a charge to the packing of the finished powder, compared to about 15 days required bythe old waterdrying method. Moreover the 'present method permits accurate control so that a high degree of uniformity in the product I present metho can be maintained, and the residual solvent can be held within much narrower limits than it can be in the old walter-drying method.

fAs an example of the application of the we have satisfactorily proceeded as follows in the treatment of powder of, 155 m/m Howitzer granulation having a finished mean web of 0.0315 inches, and a residual solvent of 2.85 to 2.9%

A treating tank-of any suitable character and having provisions for the inflow and outflow of liquid was filled 4} full of 60% ethyl alcohol solution, the charge of green powder from the cutting house was charged in, flow of 60% alcohol through the tank was started as soon as the entire charge was in, and was maintained at the rate of 5 gallons per minute per 1000 pounds of dry washing was 5% hours. All the outflowing powder and at a temperature of 25 to 31 C. until the ether content ofthe outflowing liquor was reduced to 3%%, indicating that the amount of retained solvent was that corresponding to the desired residual solventin the finished owder; the time required for this washing was 4 hours. All the outflowing liquor was collected in a still and the ether distilled off without destroying the percentage (60%) of alcohol in the alcohol-water solution and the ether-free solution was returned to storage and cooled for reuse. At the end of the washing the solution remaining in the tank was drained from the powder into the still and theether distilled off. -To remove retained alcohol on the surface and within the perforations of the powder grains fresh water was next flowed through the tank (and powder) at the rate of 7.7 gallons per minute for'1000 pounds of "dry owder until the solvent ad been reduce to the desired residual amount, 2.9%; the time required for the liquor (alcohol and water), was passed through a beer still, thealcohol (95% pure) recovered and the beer still slop run to the sewer or cooled for reuse. After the Water treatment the powder was dumped from the tank and given an air drying treatment to reduce the moisture content of the powder to the desired amount, between 1.65 to 2%; this drying being carried out in a continuous drier at a temperature of 55 C. and re uiring 12 to 13 hours.

' 11 alcohol solution stronger than 60% can if desired be used, as any desired concentration between 60 and 80% can be used to advantage in practising the method, the time of treatment for the alcohol wash and that for the water wash of course varying. When using 80% alcohol in the treatment of granulations of the 75 m/m ty e where alcohol treatment for 2 hours at the rate of 5 gallons per minute per 1000 pounds of dry to 31 C., followed by awater treatment for 2% hours at the rate of 7.7 gallons'per minute per 1000 pounds of dry powder and at a temperature of 28 to 32 C. is sufficient to reduce the residual solvent to 1.9%.

We prefer to use alcohol of less than 80% strength, and preferably use alcohol of substantially 60% strength, as, strength it is much easier to control the extraction of the ether and we avoidthe possible diflicultv of the ether being practically all removed and the residual solvent consisting mainly of alcohol, which may nearly all be given up on air drying. With the 60% alcohol the retention of ether is easily controlled and an ether-alcohol colloid, which will retain its solvent during air drying, conveniently obtained. r

It will be understood that the details of the method may be varied with the particular powder being treated, as, for example, the time of treatment, rate of circulation and so forth may be varied. The

method is of course applicable to small and after cooling, back to the washing tank.

Although we have described and expowder and at a temperature of 25 with 0% powders as for cannon powto the still where it is freed from alcohol,

- plained present method by giving speclifl"erent' conditions and to different powders without departing from the invention.

We claim: 1. The method of removing-and recovering ethyl alcohol and ethyl ether solvent from nitrocellulose powder which includes as two distinctly defined and separate washing steps,'the initial solvent-removing washi'ng step of removing ether by washing with ethyl alcohol and, as the next solvent-removing washing step the step of removing alcohol by washing with water,

2. The method of treating green nitro-. cellulose powder containing ethyl alcohol and ethyl ether solvent comprising washing with ethyl alcohol, draining the washing liquor from the powder,'thereby to substantially preclude the presence in the hereafter named water of the ether and the'alcohol contained in said liquor, washing with water,

and drying.

3. The method of removing and recovering ethyl alcohol and ethyl ether solvent from nitrocellulose powder comprising washingwith ethyl .alcohol, draining the washing liquor from the powder, thereby to substantially preclude the presence in the hereafter named water of the ether and the alcohol contained in said liquor, and washing initial washing step of washing the powder with ethyl alcohol of a strength to remove ether without substantial removal of alcohol, and, as the next washing step, the washing of the powder with water to remove alcohol substantially without removal of ether.

5. The method of separately removing and recovering from nitrocellulose powder the ethyl ether and the ethyl alcohol of the alcohol-ether solvent, the method including two distinctly defined and separate washing steps, which method comprises, initially washing the powder with ethyl alcohol of a strength to remove ether without substantial removal of alcohol, draining the washing liquor from the powder thereby to substantially preclude'the presence in the hereafter named water of the ether andthe alcohol contained in said liquor, washing the powder with water to remove alcohol substantially Without the removal of ether, and drying.

6. The method of removing and recovering ethyl alcohol and ethyl ether solvent,

from nitrocellulose powder which comprises washing the powder with ethyl alcohol at a temperature below the boiling point of ether until the solvent is reduced to an amount substantially corresponding to the desired amount of the residual solvent,

draining the washing alcohol from the powder, and washing the powder with water ata temperature below the boiling point of other until the solvent is-reduce'd to substantially the desired residual amount.

7. The'method of removing and recovermg ethyl alcohol and ethyl ether solvent from nitrocellulosepowder which comprises washing the powder with 60 to ethyl alcohol at a temperature below the boiling point of ether until the solvent is reduced to an amount substantially corresponding to the desired amount of residual solvent, draining the washing alcohol from the powder, and washing the powder with water at a temperature below the boiling point of ether until the solvent is reduced to substantially the desired residual amount.

8. The method of removing and recovering ethyl alcohol and ethyl ether solvent from nitrocellulose powder which comprises washing the powder with substantially 60% ethyl alcohol at a temperature between 25 and 31 C. until the solvent is reduced to an amount substantially corresponding, to the desired amount of residual solvent, draining the washing alcohol from the powder, and washing the powder with water at a temperature between 28 and 32 C. until the solvent is reduced to substantially the desired residual amount.

9. The method of removing and recovering ethyl alcohol and ethyl ether solvent from nitrocellulose powder which comprises washing the powder with substantially 60% ethyl alcohol at a temperature between 25 and 31 C.'until the ether content of the off-flowing liquor is reduced to substantially 3%70, draining the washing alcohol from the powder, and washing the powder with water at a temperature between 28 and 32 C.

until the solvent is reduced to substantially the desired residual amount.

In testimony whereof we aflix our signatures.

FRED W. STETSON. JESSE L. ESSEX. 

